1. Field of the Invention
The present invention relates to a process for chlorinating the 5-position of pyridine nucleus of .beta.-trifluoromethylpyridines with chlorine gas in the presence of a specific catalyst.
2. Description of the Prior Art
Recently, 5-chloro-.beta.-trifluoromethylpyridines having trifluoromethyl group at .beta.-position of the pyridine nucleus and chlorine atom at 5-position thereof have been considered to be remarkably useful as intermediates for medicines and agricultural chemicals such as herbicides, fungicides and insecticides.
5-Chloro-.beta.-trifluoromethylpyridines include 5,6-dichloro or 2,5,6-trichloro-.beta.-trifluoromethylpyridine. These compounds will be referred to as 5-chloro-.beta.-trifluoromethylpyridines.
It has been difficult to produce 5-chloro-.beta.-trifluoromethylpyridines in an industrial process. For example, the process for producing 5,6-dihalogeno-.beta.-trifluoromethylpyridine has been disclosed in WO 79/00094. The process is a small laboratory scale process and is not suitable as an industrial process. In this process, 6-amino-.beta.-methylpyridine is brominated to produce 6-amino-5-bromo-.beta.-methylpyridine and the product is diazotizated and chlorinated followed by chlorinating it under UV irradiation to produce 5,6-dichloro-.beta.-trichloromethylpyridine, and the product is further fluorinated with antimony fluoride to produce 5,6-dichloro-.beta.-trifluoromethylpyridine. The starting material in the process is, however, remarkably expensive and the operation is complicated in many reaction steps to be disadvantageous as an industrial process.
It has been succeeded in the industrial production of .beta.-trifluoromethylpyridines such as 6-chloro, or 2,6-dichloro-.beta.-trifluoromethylpyridine from .beta.-picoline and accordingly it has been studied to produce 5-chloro-.beta.-trifluoromethylpyridines from .beta.-trifluoromethylpyridines. Hereinafter, 6-chloro or 2,6-dichloro-.beta.-trifluoromethylpyridine will be referred to as .beta.-trifluoromethylpyridines. In the study, 6-chloro-.beta.-trifluoromethylpyridine is treated with ammonia water under an elevated pressure to produce 6-amino-.beta.-trifluoromethylpyridine and the product is chlorinated to produce 6-amino-5-chloro-.beta.-trifluoromethylpyridine and the product is diazotizated and chlorinated to produce 5,6-dichloro-.beta.-trifluoromethylpyridine. In this process, however, the reaction should be disadvantageous carried out under an elevated pressure in many reaction steps and moreover, the treatment of wasted water is not easy.